Our previous linkage analyses have suggested that there is a major gene on chromosome 15 which has a strong influence on reading disability. A lod score of 3.2 at 0=0.13 has been obtained between specific reading disability and chromosome 15 heteromorphisms. This study proposes to continue the linkage analysis utilizing the new restriction enzyme polymorphisms, which not only provides an independent means of verifying this linkage, but adds capabilities beyong those of traditional markers. The potential exists for localizing a site more tightly linked to the gene in question so that once a linkage has been identified, heterogeneity can be more readily detected. These unique abilities are particularly significant in studies of complex traits such as reading disability where genetic heterogeneity is anticipated. Identification of a gene or genes influencing reading will be of great value in the difinition of homogeneous subgroups based on etiology, so that meaningful assessments of specific deficits, development and prognosis, and appropriate remediation, can be done.